Ordering the wrong grip length is the most common AN bolt mistake. You pick the right diameter, the right thread — and then get a bolt that's 1/8" too short to thread a nut properly, or so long the threads extend into the shear plane. This reference tells you exactly what each dash number means before you place the order.
What "Grip Length" Actually Means
The grip is the unthreaded portion of the shank — the part that passes through the material being joined. The grip bears the shear load. The threads don't. This is not the same as total bolt length.
Total bolt length = grip length + thread length
Thread length is fixed for each bolt diameter. Grip length changes with the dash number. When you order AN4-7, you're ordering a 1/4"-28 bolt with a 1/2" nominal grip.
Why it matters: If your grip is shorter than the stack you're bolting, threads will engage inside the joint. The threads are weaker than the shank — you've turned a shear joint into a thread-failure waiting to happen. The grip must span the full material thickness.
One AN960 washer (1/16" thick) under each end is standard practice. Size your grip to accommodate the washer stack. See the AN3–AN10 Sizing Reference for washer pairings by bolt size.
How to Measure Grip
- Measure the total thickness of all material layers being joined, including any washers under the head and under the nut.
- The grip should be equal to or very slightly greater than that total thickness.
- Do not count the AN960 flat washers in the grip — you're sizing the bolt to pass cleanly through them.
- When in doubt, go one dash number longer and add a washer to fill the gap. Do not go shorter.
The Full Grip Length Chart — AN3 Through AN10
Dash numbers in 1/8" increments. Thread length is constant per diameter. All dimensions in inches.
AN3 | Diameter: 3/16" | Thread: 10-32 UNF-3A | Thread Length: 0.406"
| Dash # | Nominal Grip | Total Length |
|---|---|---|
| -3 | 1/16" (0.063) | 15/32" (0.469) |
| -4 | 1/8" (0.125) | 17/32" (0.531) |
| -5 | 1/4" (0.250) | 21/32" (0.656) |
| -6 | 3/8" (0.375) | 25/32" (0.781) |
| -7 | 1/2" (0.500) | 29/32" (0.906) |
| -10 | 5/8" (0.625) | 1-1/32" (1.031) |
| -11 | 3/4" (0.750) | 1-5/32" (1.156) |
| -12 | 7/8" (0.875) | 1-9/32" (1.281) |
| -13 | 1" (1.000) | 1-13/32" (1.406) |
| -14 | 1-1/8" (1.125) | 1-17/32" (1.531) |
AN4 | Diameter: 1/4" | Thread: 1/4-28 UNF-3A | Thread Length: 0.469"
| Dash # | Nominal Grip | Total Length |
|---|---|---|
| -3 | 1/16" (0.063) | 15/32" (0.469) |
| -4 | 1/16" (0.063) | 17/32" (0.531) |
| -5 | 3/16" (0.188) | 21/32" (0.656) |
| -6 | 5/16" (0.313) | 25/32" (0.781) |
| -7 | 7/16" (0.438) | 29/32" (0.906) |
| -10 | 9/16" (0.563) | 1-1/32" (1.031) |
| -11 | 11/16" (0.688) | 1-5/32" (1.156) |
| -12 | 13/16" (0.813) | 1-9/32" (1.281) |
| -13 | 15/16" (0.938) | 1-13/32" (1.406) |
| -14 | 1-1/16" (1.063) | 1-17/32" (1.531) |
AN5 | Diameter: 5/16" | Thread: 5/16-24 UNF-3A | Thread Length: 0.531"
| Dash # | Nominal Grip | Total Length |
|---|---|---|
| -4 | 1/16" (0.063) | 0.594 |
| -5 | 3/16" (0.188) | 0.719 |
| -6 | 5/16" (0.313) | 0.844 |
| -7 | 7/16" (0.438) | 0.969 |
| -10 | 9/16" (0.563) | 1.094 |
| -11 | 11/16" (0.688) | 1.219 |
| -12 | 13/16" (0.813) | 1.344 |
| -13 | 15/16" (0.938) | 1.469 |
| -14 | 1-1/16" (1.063) | 1.594 |
For AN6 (3/8", thread: 3/8-24 UNF-3A, thread length: 0.641") through AN10 (5/8", thread: 5/8-18 UNF-3A), dash numbers and grip increments follow the same 1/8" pattern. Thread length increases with diameter.
Dash Number Suffix: "A" and "H"
- AN4-7 = undrilled shank, standard head. Use with self-locking nuts (AN365, MS21044).
- AN4-7A = undrilled shank, "A" suffix. Standard for use with self-locking nuts.
- AN4H-7 = drilled head for safety wire.
- AN4-7 (drilled shank, no A suffix) = for use with castle nut and cotter pin. See the Castle Nut and Cotter Pin Pairing Guide.
If you're using an AN365 or MS21044 locknut, order the -A suffix. If your design calls for a castle nut and cotter pin, order without the A.
Common Mistakes
- Measuring grip from the head face to the thread start — correct.
- Measuring from head face to bolt tip — this is total length, not grip. Wrong.
- Forgetting AN960 washers — a standard washer is 1/16" thick. A stack of 2 adds 1/8". Factor this in.
- Using bolt length markings on hardware-store fasteners — AN bolt length codes are spec-specific. A bolt labeled "1/2 inch" at a hardware store is not an AN4-4.
Compare our AN bolt pricing against major suppliers at our Aircraft Spruce comparison page.